1. Field of the Invention
The present invention relates to a heat-developable photosensitive material containing an organic silver salt. It also relates to an image forming method making use of such a heat-developable photosensitive material.
2. Related Background Art
Hitherto known silver salt photography making use of a photosensitive silver halide can achieve excellent sensitivity and gradation, and is a recording technique having been most widely put into practical use. This photography, however, makes use of a wet process in the processing steps such as developing, fixing and washing, and hence has many problems on operability and safety such that it takes much labor and time for the processing and chemicals used for the processing may give anxiety for influence on human bodies.
As a countermeasure therefor, research has been extensively made in relation to dry processing photography eliminating the wet process, as disclosed in Japanese Patent Publications No. 43-4921, No. 43-4924, etc. These disclosures are concerned with a technique in which a photosensitive silver halide is used in an amount corresponding to the amount required for a catalyst and a non-photosensitive organic silver salt is used as an image forming agent. The mechanism by which the organic silver salt acts as an image forming agent can be explained as follows: (1) A silver nucleus is produced from a photosensitive silver halide as a result of exposure, and it forms a latent image. (2) The silver nucleus serves as a catalyst, for an organic silver salt and a reducing agent which cause oxidation-reduction reaction upon heating, and the organic silver salt is reduced to metallic silver, which forms a visible image.
As an example of methods of utilizing such a heat-developable photosensitive material, Japanese Patent Application Laid-open No. 55-50246 discloses a method of use as a mask. In this method, a silver image is used as a mask. Silver images formed using such conventional heat-developable photosensitive materials have been disadvantageous in that they are reddish and can not be pure-black.
Because of an advantage of the heat-developable photosensitive material over the wet-process silver salt photosensitive material in view of the fact that the former requires no wet processing, it has been sought to make contrast and raw stock stability comparable to, or more improve them than, those of the wet-process photosensitive materials (the raw stock stability is the properties by which photosensitive materials can be stored in such a state that its photographic performance immediately after manufacture is retained as it is).
Meanwhile, the present assignee has disclosed in Japanese Patent Application Laid-open No. 3-135564 a photosensitive material that utilizes light absorption of a light-absorbing organic compound to form an image. This light-absorbing organic compound is an oxidized product of a reducing agent.